New Approaches for Extending the Twentieth Century Climate Record
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Eos,Vol. 86, No. 1, 4 January 2005 With support from the U. S. National Science References Oganov,A. R., and S. Ono (2004),Theoretical and Foundation (NSF), a multidisciplinary work- experimental evidence for a post-perovskite phase Badro, J., J.-P.Ruef, G.Vankó,G. Monaco, G. Fiquet, and ″ shop organized by the Cooperative Institute of MgSiO3 in Earth’s D layer, Nature, 430, 445–448. F.Guyot (2004),Electronic transitions in perovskite: for Deep Earth Research (CIDER) was held at Shim, S.-H.,T.S. Duffy,R. Jeanloz, and G. Shen (2004), Possible nonconvecting layers in the lower man- Stability and crystal structure of MgSiO perovskite the Kavli Institute for Theoretical Physics of 3 tle, Science, 305, 383–386. to the core-mantle boundary, Geophys. Res. Lett., the University of California, Santa Barbara on Humayun, M., L. Qin, and M. D.Norman (2004), Geo- 31, L10603, doi:10.1029/2004GL019639. 12 July–6 August 2004 (http://online.kitp.ucsb. chemical evidence for excess iron in the mantle Sidorin, I., M. Gurnis, and D.V.Helmberger (1999), edu/online/earth04/). Part of the workshop beneath Hawaii, Science, 306, 91–94. Dynamics of a phase change at the base of the focused on the post-perovskite phase transi- Iitaka,T., K. Hirose, K. Kawamura, and M. Murakami mantle consistent with seismological observations, (2004),The elasticity of the MgSiO post-perovskite tion, and highlighted the emerging multidisci- 3 J. Geophys. Res., 104, 15,005–15,023. phase in the Earth’s lowermost mantle, Nature, plinary challenges. Tsuchiya,T., J.Tsuchiya, K. Umemoto, and R. M. 430, 442–445. CIDER provides a promising community Wentzcovitch (2004a), Elasticity of post-perovskite Lay,T., E. J. Garnero, and Q.Williams (2004), Partial MgSiO ,Geophys.Res.Lett.,31,L14603,doi:10.1029/ organization for communication and collabo- melting in a thermo-chemical boundary layer at 3 2004GL020278. ration across the relevant disciplines, and the the base of the mantle, Phys. Earth Planet. Inter., Tsuchiya,T., J.Tsuchiya, K. Umemoto, and R. M.Wentz- NSF Program for Cooperative Studies of the 146, 441–467. covitch (2004b), Phase transition in MgSiO per- Earth’s Deep Interior is a key source of research Mao,W.L., G. Shen,V.B. Prakapenka,Y.Meng, 3 ovskite in the Earth’s lower mantle, Earth Planet. Sci. A. J. Campbell, D.L. Heinz, J. Shu, R. J. Hemley,and support. Special sessions recently held at the Lett., 224, 241–248. 2004 AGU Fall Meeting, and upcoming at the H.-K. Mao (2004), Ferromagnesian postperovskite ″ 2005 Joint Assembly,are another valuable silicates in the D layer, Proc. Natl.Acad. Sci. U.S.A.,101, 15,867–15,869. means by which to inform and catalyze inter- Matyska, C., and D.A.Yuen (2004),The importance of Author Information actions across the community. radiative heat transfer for superplumes with a deep mantle phase transition,Earth Planet. Sci. Thorne Lay,University of California, Santa Cruz; Lett., 125, 255–266. Dion Heinz, University of Chicago, Ill.; Miaki Ishii, Murakami, M., K. Hirose, K. Kawamura, N. Sata, and Y. Institute of Geophysics and Planetary Physics, Acknowledgments Ohishi (2004), Post-perovskite phase transition in Scripps Institution of Oceanography,University of MgSiO3, Science, 304, 855–858. California, San Diego; Sang-Heon Shim, Massachu- The authors thank Barbara Romanowicz Nakagawa,T.,and P. J.Tackley (2004), Effects of a per- setts Institute of Technology,Cambridge; and Jun and Adam Dziewonski for organizing the 2004 ovskite-post perovskite phase change near core- Tsuchiya,Taku Tsuchiya, Renata Wentzcovitch, and CIDER workshop, which was partially support- mantle boundary in compressible mantle David Yuen,University of Minnesota,Minneapolis ed by NSF under grants PHY99-07949 to the convection, Geophys. Res. Lett., 31, L16611, For additional information, contact T.Lay; Kavli Institute and EAR-0215587 to CIDER. doi:10.1029/2004GL020648. E-mail: [email protected]. Although the notion is widespread among New Approaches for climate scientists that there were no operational upper air measurements before about 1948, this is not the case (Figure 1). Radiosonde Extending the Twentieth observations have been made since the mid- 1930s. Prior to the radiosonde era,weather bal- Century Climate Record loons with graphical registering devices were used.Even more common were kite soundings or aircraft measurements up to 4 or 5 km alti- PAGES 2,6 transition to the “modern era”of climatology, tude.Pilot balloons have been launched rou- Studying twentieth century climate is a key which started after World War II.The reasons tinely since the early twentieth century to to understanding future climate change. Rela- are manifold and include military secrecy; obtain information on upper level winds.In tively little is still known,however,about climate interrupted international collaboration; politi- addition to meteorological measurements, variability in the first half of the century.Much cal and institutional changes during and fol- spectrographical total ozone observations could be learned from the relatively large cli- lowing the war; and,sometimes,simply neglect. reaching back to the 1920s can be used to matic variations that occurred during that first Yet,these data can still be found today on derive indirect information on stratospheric half,including the decade-long “Dust Bowl” paper in various meteorological archives.With dynamics. droughts of the 1930s and the warming of the new numerical and statistical techniques The total amount of data is small by current Arctic from 1920 to 1945. becoming available,these archives now could standards,but it is non-negligible.It is estimated Poor digital data availability prior to around be fruitfully mined for climate research. that several million pilot balloons were launched 1948 has hindered previous work to understand Data availability is comparably good for prior to 1948, and there were several hundred these important climatic variations. meteorological observations at the Earth’s sur- thousand radiosonde ascents and aircraft Several projects now are focusing on digitizing face, which have been used continuously to flights (Figure 1). earlier manuscript observations to create three- study past climate variability.Several ongoing Significant fractions of these data are dimensional,gridded meteorological data sets projects are increasing the data quality and currently being digitized and processed by for the first half of the twentieth century. quantity [e.g.,Worley et al.,2005].Surface data, organizations such as the U.S.National Climate These data sets are likely to provide further however,do not suffice to fully understand Data Center (NCDC), the National Center for insights into processes governing interannual- the mechanisms governing large-scale climate Atmospheric Research (NCAR),and the World to-interdecadal large-scale climate variability. variability. Data Center (WDC) for Meteorology in Meteorologists, geophysicists, navy pilots, Upper air data are needed for accurate Obninsk, Russia.Additional work is done by ship crews,and numerous volunteer observers descriptions of important dynamical features scientists at the Swiss Federal Institute of collected enormous amounts of atmospheric such as the positions of the jet streams, the Technology (ETH) Zürich in the framework of data in the first half of the twentieth century, planetary wave structure, and the strength of a Swiss National Science Foundation project sometimes under extreme and dangerous the stratospheric polar vortex.Yet,gridded led by the first author. conditions.A large fraction of these data, upper air data sets currently are available only Re-evaluating historical upper air data is especially upper air data, never made the for the second half of the twentieth century; demanding work.After digitizing the numbers they are based largely on radiosonde data, from paper,the data need to be corrected for BY S. BRÖNNIMANN,G.P.COMPO,P.D.SARDESHMUKH, and since 1973, on radiosonde and satellite various instrumental errors,a task made difficult R. JENNE, AND A. STERIN data (Figure 1). by the lack of good background information. Eos,Vol. 86, No. 1, 4 January 2005 Environmental Sciences, sponsored jointly by NOAA and the University of Colorado,Boulder]/ CDC) in Boulder,Colorado, new techniques such as the “ensemble square root-filter” (EnSRF) [Whitaker and Hamill, 2002] have been developed and tested. Figure 2 shows Northern Hemispheric 500-hPa (hectopascals) geopotential height fields for 14 December 2001,0000 UTC,obtained from a conventional assimilation of all available data (surface, upper air,and satellite; left panel), and an EnSRF assimilation using only a limited number of surface pressure observations (right panel), mimicking the network of land stations and marine observations of the year 1915 (black dots) [Whitaker et al., 2004]. The two fields are very similar; their differ- ence (the error of the “reanalysis”) is of com- parable magnitude to current 2.5-day forecast errors. Overall, the results of Whitaker et al. suggest that useful upper air circulation analyses up to the middle troposphere may already be feasible with the available digitized data, even for times prior to any upper air observations. Better results could be expected if historical upper air data were also to be included.The goal of the efforts at NOAA-CIRES/CDC is to produce a new reanalysis data set for the entire twentieth century to present. Another approach to deriving fields from scattered upper air observations is reconstruc- tion,i.e., by using statistical